1. Field of the Invention
The field of the invention relates to screw-type fasteners in general, the heads of which are provided with inverted T-shaped slots which are adapted to be engaged by the T-shaped blade of a driver.
2. Description of the Prior Art
Applicant is aware of the following relevant prior art:
U.S. Pat. Nos. 3,897,812 and 3,923,008 of E. T. Arnn which disclose a screw driver, the blade end of which is flared outwardly as at 32 to provide "bites" 30, the overall spacing of which are equal to the width of a rectangular slot provided in the head of a fastener, said "bites" increasing the effectiveness of the blade in gripping the vertical side walls of a slot in the screw head.
U.S. Pat. No. 1,476,653 of J. R. Stanton discloses a screw driver, the blade of which comprises two pairs of reversing beveled faces 14 which converge toward a central restricted portion 15, said blade being adapted to be inserted axially into the transverse groove 17 of a screw head 16, which groove has a narrow central portion 18 to correspond to the reversed beveled faces 14 of the blade.
U.S. Pat. No. 3,026,920 of B. H. York discloses a screw driver having a driving tip which is adapted for use with fasteners having undercut driver-receiving recesses having contours as disclosed in FIGS. 12-18 and wherein the driving tip 23 of the screw driver is shaped whereby to be introduced in an axially, end-wise direction into the recessed head of a screw fastener of the type which is adapted to be countersunk into a supporting surface.
U.S. Pat. No. 1,997,422 of H. Lorenzen, et al, discloses a countersunk screw and a driver therefor wherein the driver is adapted to be interlocked relative to a transverse slot in the screw head. The end face 12 of the driver bit is curved outwardly about a point along the lateral axis of the driver as a center, and the angle of divergence of the sides 4 from the vertical is less at the edges than at the middle of the bit whereby to provide the edge portions of the bit somewhat thinner than the width of the slot in the head of a screw. The end of the bit is adapted to be inserted edgewise into the screw slot, and after the screw has been completely driven and countersunk into the work, the driver is separated therefrom by tilting the driver so as to place an edge portion of the face of the bit in the open face of the slot after which the driver is then manipulated to force the remaining portion of the face of the driver bit to become disengaged from the screw slot. The relationship of the bit and screw slot is such that a screw may be readily carried on the end of the bit preparatory to a screwing operation, and at the end of an unscrewing operation, the screw will be carried on the end of the screw driver bit to prevent its being accidentally dropped until removed by an operator.
U.S. Pat. No. 2,566,055 of M. Daderko, et al, discloses a screw having a slotted head and a driving tool therefor wherein the screw head is provided with a transverse slot having a centrally disposed concave portion 20 and wherein the side walls of the slot are undercut to provide a dovetail cross section as illustrated in FIGS. 1 and 2 thereof. The tip of the screw driver is provided with a bit 28 having opposite side faces 30 which lie in convergent planes as they recede from the shank 26. Faces 30 are flat so that at their convergent ends they form a relatively narrow edge which is adapted to enter the slot in the screw head. A lip 32 extends outwardly from one face 30 of bit 28, said lip adapted to engage an undercut portion of the groove in the screw in substantial alignment with shank 26. The tip of the screw driver is engageable with and removable from the screw slot by tilting the shank of the screw driver as in FIG. 2, whereby to initially introduce extending lip 32 into the slot whereby said lip will be disposed in contacting relationship with one side of the dovetail groove of the screw head when the shank of the screw driver is disposed in axial alignment with the screw.
U.S. Pat. No. 306,492 of G. W. Jackman discloses a screw, the head of which is provided with a pair of transverse splines such as illustrated in FIGS. 2 and 4, the central undercut portions of which are adapted to be selectively engaged by undercut portions of the jaws of a screw driver wherein said jaws are movable toward and away from one and other from non-engaging to engaging relationship with the central undercut portions of the pair of splines in the screw head. When the jaws of the driver are disposed in engagement with the spline portion of the screw head, accidental or unintentional disengagement of the screw is effectively precluded.
U.S. Pat. No. 3,825,048 of M. K. Triska discloses a screw head and driving tool therefor which are releasably coupled together by means of a pair of radially shiftable anchors each of which have an outwardly and downwardly tapered outer surface 25, and an inner axial surface 28, said anchors are held in alternate engagement and disengagement with a complimentary screw slot by a driver blade 22 shiftable longitudinally between said anchors. The screw slot is undercut to prevent displacement of the tapered driving tool from the screw head when the anchors are set in engaged condition and to permit disengagement when the anchors are set in disengaged condition.
U.S. Pat. No. 449,037 of G. T. Chapman discloses a wood screw the head of which is provided with a transversely extending slot, the lower portion of which is defined by a cylindrical groove the radius of which is greater than the width of the upper portion of the slot. The reason for the slot is to strengthen the head against the tendency of breakage by the screw driver and so that it will retain the filling of putty generally applied in finishing interior work.
U.S. Pat. No. 2,301,590 of R. Signorelli discloses a screw driver which comprises a pair of laterally spaced bit members 4 the lower end of each of which terminates in outturned lips 6 which are adapted to be received within the undercut transverse slot B in the head of a screw, the outer ends of each of said bits are forced apart as the bits are shifted upwardly axially to and along a flat shank 2 which is disposed between said bit members. The bit members are thus forced apart, engage and substantially fill the undercut slot of the fastener member.
U.S. Pat. No. 2,684,094 of J. Lissy discloses a non-slip screw driver and screw head wherein the bit of the screw driver is provided with outwardly flared projections 17 and 18 which are adapted to fill undercut spaces 15 and 16 of the opposite walls 13 and 14 of the slot 12 in the screw head 11. The flared projections 17 and 18 of the screw driver engage the aforesaid undercut space of the side walls of the slot of the head incident to turning of the screw driver after it has been introduced in an endwise axial direction into the screw slot.
U.S. Pat. No. 1,782,981 of J. A. Anderson and U.S. Pat. No. 1,741,349 of R. R. Sullivan each relate to and disclose screw drivers the bits of which have been provided with serrations which are adapted to abut against the walls of a slot in the head of a fastener.
U.S. Pat. No. 2,808,087 of R. M. Vaughn; U.S. Pat. No. 3,120,251 of B. H. York; and U.S. Pat. No. 2,677,985 of R. M. Vaughn each relate to and disclose screw drivers the bits of which are shaped whereby to selectively and interlockingly engage the transverse slots of the head of fasteners wherein the bits of the screw drivers are inserted in an endwise axial direction into the screw head slots.